Investments - Summary of Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments [Abstract]
Fixed maturity securities, gross realized gains	$ 386	$ 445	$ 906	$ 1,033
Fixed maturity securities, gross realized losses	0	(9)	(1)	(494)
Fixed maturity securities	386	436	905	539
Bank loan participations, gross realized gains	24	79	357	229
Bank loan participations, gross realized losses	(3,506)	(6,056)	(14,484)	(9,056)
Changes in fair values of bank loan participations	9,741	0	(7,636)	0
Bank loan participations	6,259	(5,977)	(21,763)	(8,827)
Equity securities, gross realized gain	13	11	13	11
Equity securities, gross realized losses	0	(78)	(170)	(96)
Changes in fair values of equity securities	2,374	3,251	(6,895)	8,700
Equity securities	2,387	3,184	(7,052)	8,615
Short-term investments and other, gross realized gains	27	1	76	5
Short-term investments and other, gross realized losses	0	(1)	(1)	(1)
Changes in fair values of short-term investments and other	(130)	0	(50)	0
Short-term investments and other	(103)	0	25	4
Total	$ 8,929	$ (2,357)	$ (27,885)	$ 331